A compressed-air feed installation is used in vehicles of all types, in particular for feeding compressed air to an air spring installation of a passenger motor vehicle or of a utility vehicle. Air spring installations may also comprise ride-height control devices by means of which the distance between vehicle axle and vehicle body can be adjusted. An air spring installation of a pneumatic compressed-air feed system as mentioned in the introduction comprises a number of air bellows pneumatically connected to a common line (gallery), which air bellows can, with increasing filling, lift the vehicle body and, with decreasing filling, lower the vehicle body. Such a system is used for example in an off-road vehicle and in a sports utility vehicle (SUV) or in a utility or passenger transport vehicle.
To ensure long-term operation of the compressed-air feed installation, the latter has an air dryer by means of which the compressed air can be dried. The accumulation of moisture in the compressed-air feed system, which can otherwise, in the presence of relatively low temperatures, lead to valve-damaging ice crystal formation and other undesired effects in the compressed-air feed installation and in the pneumatic installation, is thus avoided. An air dryer has a drying agent, normally a granulate filling, which can be flowed through by the compressed air, such that the granulate filling—in the presence of relatively high pressure—can, by adsorption, take in moisture that is contained in the compressed air. Here, it has often proven to be expedient for the dry granulate to be accommodated in a dryer cartridge which has a dryer bed for conducting a compressed-air flow.
A compressed-air feed installation for use in a pneumatic compressed-air feed system having a pneumatic installation, for example having an air spring installation as described above, is operated with compressed air from a compressed-air supply, for example at a pressure level of 5 bar to 20 bar. The compressed air is provided to the compressed-air supply by means of an air compressor (compressor), in the present case having a reciprocating-piston machine, preferably having a two-stage or multi-stage piston compressor.
In the case of a compressed-air feed installation for a compressed-air feed system in a vehicle, the compressed-air supply which is fed by the air compressor is, on the one hand, pneumatically connected to a compressed-air connection for the feed of the pneumatic installation and, on the other hand, pneumatically connected to a ventilation connection. By means of a ventilation valve arrangement, the compressed-air feed installation and/or the pneumatic installation can be ventilated by discharging of air in the direction of the ventilation connection.
The reciprocating-piston machine in the air compressor (compressor) of the compressed-air supply is generally driven by means of a drive motor, the drive power of which is transmitted via a crankshaft and via one or more connecting rods to one or more pistons of the preferably two-stage or multi-stage piston compressor—a piston runs in a sealed manner in a cylinder during operation. The drive of the reciprocating-piston machine in the air compressor (compressor) of the compressed-air supply may also be realized for example by means of a belt drive.
In this way, ambient air that is drawn in, or intake air supplied from some other compressed-air source, is compressed. For this purpose, so-called twin piston compressors have basically proven expedient, that is to say two-stage piston compressors whose two pistons are driven by means of two connecting rods that are respectively assigned to said pistons, which connecting rods are in turn aligned exactly along a cylinder axis which is preferably aligned exactly parallel to and centrally symmetrical with respect to cylinder lining surfaces in the cylinder displacement chamber for the pistons.
Depending on the demanded dynamics and pressure loading, a two-stage or multi-stage compressor of said type or of some other type may, during operation, generate increasing operating noises which—as has been found—may be caused significantly by transmission of body-borne sound through the crank drive inter alia into the drive motor of the compressor or into the housing thereof. It is desirable to realize improved acoustics and a nevertheless reliable connecting-rod drive in a compressor in the form of the stated reciprocating-piston machine. This should in particular also be sufficient for a particularly low noise level in the passenger motor vehicle sector.
For example, DE 10 2004 020 104 discloses a twin compressor with symmetrically mounted double pistons for a compressor, having an elongate piston support which has a piston on each end, and having a connecting rod which runs approximately parallel to the piston support and which, by means of a bearing, is mounted rotatably on a pin of the piston carrier and which, at a distance therefrom, is mounted by means of a connecting-rod bearing on an eccentric of a drive device. The piston carrier comprises, in a central region extending between the two pistons, an intermediate space which is dimensioned for accommodating the connecting rod in freely movable fashion and in which the connecting rod is received in freely movable fashion.